1. Introduction
The present invention relates generally to ear wax barriers and acoustic attenuators. More particularly, the invention relates to a barrier that reduces the amount of ear wax that may enter the sound channel of a hearing aid device, such as "in-the-ear" or "canal" type hearing aids or acoustical resonators, and that may furthermore effectively modify the frequency response of the hearing aid device.
Most hearing aids include a housing, or shell, that holds the components of the aid. The shell of many aids are designed to rest within the ear canal of a user. The shell of an electronic hearing aid may hold, for example, a microphone, amplification circuitry, and a receiver. The microphone is exposed to sound signals from outside of the aid and responsively creates an electrical signal. The electrical signal may be sent to the amplifying circuitry or other electrical aid components. Such components, in turn, supply a signal to the receiver, and the receiver responsively creates sound.
In many electronic hearing aids, the sound travels from an output port of the receiver, through a sound channel in the aid, and out of the aid through an output port in the shell of the aid. The sound from the shell output port may then travel through the user's ear canal and cause the ear drum to vibrate.
The ears of most hearing aid users naturally secrete a substance referred to as cerumen or ear wax. While the ear wax cleans the internal structure of an ear, it also tends to flow into the sound channel and receiver of the hearing aid. Upon entering the receiver, the ear wax interferes with, or prevents, the proper operation of the receiver.
Small, cosmetic "in-the-ear" aids and "canal" aids (which typically lay at least partially within the user's ear canal) have now been developed. With such aids, however, the physical volume inside of the hearing aid available for components is reduced. This is particularly true, for example, when the interior of the user's ear is relatively small.
Furthermore, the technology associated with hearing aid manufacture frequently involves fabricating the shell out of plastic. The shell is contoured to the shape of the inner surface of the ear. The thickness of the shell is dictated by the requirement that the shell physically maintain its structural integrity and protect the aid components inside. The wall thickness of the shell, however, reduces the physical volume inside the hearing aid available for components. The reduced volume increases the need for a means for attenuating sound signals with smaller components.
The resulting limited space within the hearing aid available for components generally requires that the receiver be positioned as deep as possible in the user's canal. However, such positioning of the hearing aid within the canal brings the receiver output port into closer proximity to the ear canal environment containing the wax-generating tissue inside the ear canal.
Thus, while the introduction of in-the-ear and canal aids has improved the acceptance of hearing aids by the hearing-impaired public, such hearing aids have created problems associated with smaller components and greater ear wax build up within the hearing aid. Each of these two problems is discussed below.
2. Wax Migration--Prior Art
As those of the ordinary skill in the art will acknowledge, ear wax migration has been recognized as a difficult problem. The migration of wax into the sound channel and receiver of hearing aids substantially increases the susceptibility of many receivers to clogging. The progressive, gradual clogging of the receiver results in the reduction of acoustic gain and in power output by the receiver, sometimes culminating in the complete failure of the aid to provide amplified sound.
The degradation or failure of performance of the aid is annoying to the user. When wax blockage occurs, the hearing aid may require complete disassembly so that the receiver may be cleaned or replaced. Of course, bringing the hearing aid to a service center for disassembly and possible replacement of the receiver is both inconvenient and expensive for the user.
A number of presently available systems are poorly suited to guard against ear wax buildup in the receiver of a hearing aid. Some "barrier" designs use a fine mesh screen in the sound channel between the receiver and the outside of the hearing aid. Such screens suffer from the deficiency, however, that if the screen size is made sufficiently small to protect the receiver from wax migration, the screen holes will eventually be clogged by the wax. When mesh is made more coarse, however, wax will not be as effectively prevented from migrating across the screen barrier to the receiver.
Other systems for preventing wax migration into a receiver include providing a single aperture, of a small cross sectional area, between the receiver and the outside of the aid. Other systems involve the replacement of a cellular synthetic material between the receiver and outside of the aid. Such designs often suffer from the same deficiency of not simultaneously achieving both a long-term barrier to wax migration and still preventing the clogging of wax over the life of the aid.
Such porous barriers, thus, generally result in an unsatisfactory trade-off between resistance to wax clogging of the barrier itself, on the one hand, and the prevention of wax migration into the receiver on the other. While a small aperture barrier may prevent wax migration, it will also clog. Large apertures may not clog, but they also will not be as effective in blocking wax.
Small pore barriers placed in the pathway between the receiver and the output port of the hearing aid may cause increased acoustic impedance Increased impedance may result in an undesired change in the frequency response in output pressure levels delivered by the receiver. While it may often be desirable to modify the frequency response of a hearing aid in order to better meet the needs of a particular hearing aid user, such modification should not occur haphazardly because of wax buildup. Planned modification of the frequency response, however, often involves disassembling the aid and altering the internal structure of the aid.
3. Acoustic Attenuation--Prior Art
As is also recognized by those of ordinary skill in the art, it is often advantageous and desirable to smooth out the peaks in the receiver response characteristics, and otherwise attenuate the acoustic response of an aid. See, for example, the damped and undamped receiver output characteristics shown in FIG. 1. Such attenuation may improve the sound quality of the aid and thus improve the usefulness of the aid to the hearing impaired.
Some prior art devices, for example, use a barrier inserted in a hearing aid sound passageway distal from the receiver output port. The barrier may consist of a porous element, providing a fixed acoustic response. Such a barrier may smooth out the peaks of the frequency response of a hearing aid receiver in a substantially fixed, non-varying manner. However, many such elements are not easily removed and replaced in the field, nor are the damping characteristics of the barrier easily altered.
As is recognized in the art, variable damping is often desirable to accommodate the requirement of persons with different hearing requirements and impairments. Also, it is often desirable for a trained hearing aid dispenser (and not the hearing aid user) to adjust the damping characteristics of such a barrier and to clear the aid of excess wax built up within the aid.
The ability to adjust the hearing aid frequency response in the field is particularly important, since different wearers require different frequency response characteristics, and such characteristics most frequently cannot be determined in advance. The characteristics can frequently only be determined based on the actual experience of the wearer. The aid dispenser must be able to adjust the frequency response of the aid in the field for proper operation of the aid.
Thus, it is desirable for a single unit to provide the twofold function of providing variable acoustic damping and blocking potentially harmful ear wax. Moreover, such a device, which combines both features, should simultaneously allow easy adjustment and removal by a hearing aid dispenser.